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Frequently Overlooked Features in Abaqus

SIMULIA Great Lakes Regional User Meeting

Oct 12, 2011

Brad Heers

Technical Marketing, Automotive

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A true story…...from the “old days” of CAE

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Looking at Example Problems

Explicit Dynamics for Vehicle Crash Cellphone drop?

Soil mechanics for Civil Engineering Analysis of wet and dirty diapers?

Cohesive elements for fracture analysis Adhesives for food preservation?

Iterative Solver for automotive engines Geomechanics of large oil fields?

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versus today…

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Abaqus 6.11

Contains over 110 new features

Significantly expanded multiphysics

See Release Notes for comprehensive

listing of everything that is new

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Our “Dilemma”

Many new features every Abaqus release Not enough time for SIMULIA to talk about every feature

Not enough time for users to read every Example Problem

CAE has become “mission-critical” and very busy This is good for our personal employment

But does not provide enough time to “imagine new uses”

What are the “Really Useful Features” Or at least some of them?

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Discussion Topics

Elements

Solution Sequences and Solution Features

Performance and Efficiency

Contact

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Discussion Topics

Elements

Solution Sequences and Solution Features

Performance and Efficiency

Contact

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C3D10I: General-Purpose Tetrahedral Element

I = “Improved Surface Stress” Not Incompatible Modes

Integration points at the corner nodes Thus stresses are calculated directly on the surface

Removes extrapolation issues

Removes need for membranes for stress recovery

Improved bending response

Slight performance degradation relative to C3D10

Good in contact with surface to surface formulation

Introduced in Abaqus 6.9

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C3D10I: General-Purpose Tetrahedral Element

Key features Provides accurate surface stress predictions

Suitable for bending-dominated problems

Handles incompressible material behavior

Works well with contact

Some added computational expense

Benefit Simplifies element selection

C3D10IC3D10M

Analytical solution:

38,400 psi

C3D10I matches

analytical solution

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Elastoplastic knuckle

C3D10I: General-Purpose Tetrahedral Element

Note no extrapolation

error in stress contour plot

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C3D10I: General-Purpose Tetrahedral Element

Copper rod impact Good agreement with Abaqus/Explicit results (Benchmark manual).

C3D10M cannot complete simulation.

Initially no Lagrange Multipliers present. As material starts to flow

plastically they are created.

Initial configuration 40μs 80μs

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C3D4H: First Order Hybrid Tetrahedron

Improved element formulation Reformulated the volumetric constraint

Reasonable element choice for certain problems with

extreme deformations: Overloaded bushings

Surface wrinkling

Allows one to extend to high-deformation problems in

/Standard analyses This is still a linear tetrahedron

Important to first compare against a quadratic element mesh

Improved in Abaqus 6.7

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C3D4H: First Order Hybrid Tetrahedron

First-order hybrid tetrahedron Improved C3D4H formulation avoids

volumetric locking in compressible

and nearly incompressible materials

More robust in geometrically

nonlinear highly confined regions

Courtesy of Freudenberg Forschungsdienste KG and

Vibracoustic GmbH & Co KG

Contact PD Dr.-Ing. Herbert Baaser,

(Herbert.Baaser@Freudenberg.de)

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Connectors

Some specific usage that is often overlooked…

Bushing Connectors Very sophisticated 6 degree of freedom coupling

Cross-coupling terms can be dependent and co-dependent

Connectors as kinematic constraints Far superior to MPCs

o Better convergence

o Ability to extract forces, moments and other outputs directly

o No artificially high residuals

Introduced in Abaqus 6.1, progressive enhancements

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Discussion Topics

Elements

Solution Sequences and Solution Features

Performance and Efficiency

Contact

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Implicit Dynamics

Very good for certain quasi-static problems in

which the timescale is measured in seconds

but statically unstable Rubber tracks

Belt drives

“Snap-fit” problems

Keyword: “*DYNAMIC, Application=… ” quasi-static (for aggressive damping in quasi-static models)

moderate dissipation (for moderate damping—”dynamic”

problems for which contact does not need most accurate

precision)

transient fidelity (for most accurate solution—truly “dynamic”

problems)

Introduced in Abaqus 6.9EF

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Implicit Dynamics

Important to check whether model is “static” at the end of

a quasi-static analysis

A good debugging tool for problematic static analyses Dynamic solution may give insight to the static difficulties

Often a good “standard practice” tool for well-understood

quasi-static problems Often a superior solution to quasi-static problems currently being run in

/Explicit

Considerations for usage

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FromNastran: Nastran Translator to Abaqus

Translator from Nastran bdf to Abaqus inp Goal is to replicate equivalent mechanics as defined in runnable Nastran

model

Strong focus on automotive models initially This has been enhanced over subsequent releases

Focused on major Nastran sequences SOL 101, 103, 108, 111

“Customizable” for user and/or company needs Achieved via command line or environment file options

Introduced in Abaqus 6.2; enhanced every release

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Unsymmetric Solver

Often necessary for certain problems Finite sliding contact problems

o Curved surfaces and friction often lead to unsymmetric terms

o Friction forces often give rise to significant unsymmetric terms

Large deformation problems with “follower loads” (pressures, etc.)

Unsymmetric solver is more expensive than symmetric

solver for each pass However, often there are fewer passes for an unsymmetric solve, resulting

in faster runs

Unsymmetric often will solve analyses for which symmetric solver cannot

converge

Long-time feature which is not often appreciated

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Discussion Topics

Elements

Solution Sequences and Solution Features

Performance and Efficiency

Contact

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AMS Available to All Users

Large-scale eigensolver delivered as part of Abaqus Available as SMP parallel

Capable of solving 10M+ dof, 10K+ modes Highly-competitive performance

Also applicable for smaller models (500Kdof, 500 modes)

Good for nearly all Abaqus linear dynamics procedures

Introduced in 6.6, available with no charge as of 6.10

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Linear Dynamics

Very efficient when compared to other solvers Very strong serial capability

Near-linear SMP scaling for large problems

Compatible with Abaqus nonlinear analyses Able to capture pre-loading and manufacturing effects

Contains all known commercial damping models for structural dynamics Including frequency-dependent damping and stiffness

Includes structural-acoustics in one code

Rewritten over the last several releases of Abaqus

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Exterior Node and Element Output

Typically only surface output is needed Maximum stresses and strains

“Envelope” of displacements

Available as a parameter for output requests *ELEMENT OUTPUT, EXTERIOR

*NODE OUTPUT, EXTERIOR

Especially for large cast continuum models (powertrain),

this may result in significantly less output

ODB File Size Reduction! (Abaqus 6.10EF)

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Output at time intervals in Standard

Output at critical time intervals Can enforce time intervals or at nearest time intervals

Saves trouble of dividing into multiple steps

Keyword: “*TIME POINTS”

Example use-case: “Load to 10 KN, and monitor at every

1 KN interval” Without time points, this requires 10 distinct steps

With time points, this is a single step

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Discussion Topics

Elements

Solution Sequences and Solution Features

Performance and Efficiency

Contact

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Penalty Contact

Default for finite sliding surface to surface contact

Penalty=nonlinear may help convergence for some types

of problems

“Structural contact” (for transferring loads)—scaling this

down can lead to better convergence

A useful modification for certain contact problems

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Contact Improvements: No need for C3D10M

C3D10M was originally designed to give better contact

results over the C3D10 element These elements were more expensive and incompatible with other 2nd

order elements

Do not work with embedded elements

Improvements in contact make these elements generally

unnecessary in Abaqus/Standard Previous contact issues for C3D10 have been addressed through contact

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Surface Smoothing in Contact

Important when contact pressure accuracy is important

Improves accuracy and convergence for certain simply

geometries Spherical shapes in contact

Cylindrical shapes in contact

Generated automatically in Abaqus/CAE when geometry

is available

Introduced in Abaqus 6.8

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Surface Smoothing in Contact

Axisymmetric geometries often require accurate

contact pressure predictions Bolts, pins, pistons, cylinders, …

Geometry corrections can improvement accuracy Automatically applied in Abaqus/CAE

Example: Cone-shaped interface

Without correction With correction

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General Contact

Can be used to define ALL contact in the model (similar

to Explicit) Some computational overhead with this approach

Also effective when used in conjunction with contact

pairs on a “pair-by-pair” basis Define contact pairs that are critical, and automatically utilize latest

algorithms

Edge contact is now available in general contact

Available in /Standard since 6.9EF

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And now, a bold prediction…

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Bold Prediction

GPGPU Scalability is boring… But sometimes really powerful things ARE boring

Consider the 4.5 Mdof model Total run time ~ 2x faster vs. 4 core

Abaqus 6.11 “Future Overlooked Feature”

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0.5

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1.5

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2.5

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0.9 1.1 1.4 1.5 3.1 4.5

Speedup

4 cores vs. 4 cores + GPU

Problem size in MDOF

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GPGPU Scalability

Economic implications of this speedup

With a 4 core analysis (using 8 tokens) as baseline…

To run 2x faster on “default” hardware would require 8-12 core in hardware + 12-14 tokens

+100-150% hardware cost and +50-88% token cost of baseline

To run 2x faster on with GPGPU chip would require 4 core + 1 GPGPU in hardware + 9 tokens

~+100% hardware cost and ~+10-15% token cost of baseline

It is necessary to consider these implications in future IT

decisions

Example use case (very problem-dependent!)

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GPGPU Scalability

Looking at this on a per-job basis…

To run 2x number of jobs on “default” hardware would

require Equivalent or slightly-higher hardware cost

75-90% of token cost as baseline (10-25% savings per run)

To run 2x number of jobs with GPGPU chip would

require Equivalent hardware cost

55-60% of token cost as baseline (40-45% savings per run)

…another way of looking at this same data

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Summary

Each Abaqus release averages >100 new features

Many very powerful features are not widely utilized Especially “industry-specific” features

Some ideas to help “discover” additional features Talk to your local office—describe the engineering problem

o Rather than simply describing keywords

Speak to your colleagues (especially the newer users)

Talk to Abaqus users outside your industry and domain

o Sometimes their “old features” may be your “new features”

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Thank you!